1. Field of the Invention
The present invention relates generally to the field of semiconductor technology. More specifically, it relates to one-time electrically programmable antifuse technology for use in field programmable logic applications. Still more specifically, the present invention is directed to a novel electrostatic discharge ("ESD") protection device for use during the fabrication of antifuses having a top electrode formed of polysilicon and a method of fabricating such an ESD protection device.
2. The Prior Art
Polysilicon ("Poly")/Oxide--Nitride--Oxide ("ONO")/N+ diffusion antifuse has long been a primary choice for production antifuse structures. Essentially it consists of a top electrode formed of Poly, an antifuse material layer consisting of a sandwich of Silicon dioxide (SiO.sub.2), Silicon nitride (SiN), and SiO.sub.2 and a lower antifuse electrode consisting of an N+ diffusion region. Antifuses of this type are described in U.S. Pat. No. 4,823,181 to Mohsen et al., entitled PROGRAMMABLE LOW IMPEDANCE ANTI-FUSE ELEMENT and U.S. Pat. No. 4,899,205 to Hamdy et al., entitled ELECTRICALLY-PROGRAMMABLE LOW-IMPEDANCE ANTI-FUSE ELEMENT. Such antifuse structures exhibit excellent leakage and reliability characteristics, and are thus preferred for user-programmable antifuse applications.
During the fabrication process used for manufacturing antifuse elements, the wafer is exposed to environments which are potentially harmful to the antifuse material positioned between the lower and upper antifuse electrodes. For example, reactive ion plasma etching techniques employed to define small geometry features can result in the accumulation of large static charges giving rise to high voltages across sensitive areas in the integrated circuit being fabricated.
Antifuse materials which are engineered to rupture at predictable (and often relatively low) voltages are very sensitive to this phenomenon and the static charge buildup occurring during processing can easily damage the antifuse device and alter its electrical characteristics without any predictability. The resulting damaged antifuse device will therefore have unpredictable characteristics both with respect to breakdown voltage and with respect to long term stability in either the "on" (conducting) or "off" (non-conducting) states.